Explosive cord and assembly



P 1965 R. J. MILLER 3,207,073

EXPLOSIVE CORD AND ASSEMBLY Filed Dec. 21, 1962 FIG.!

INVENTOR ROSS JAY MILLER BY BT1 ggt ATTORNEY United States Patent 3,207,073 EXPLOSIVE CORD AND ASSEMBLY Ross Jay Miller, Franklin Lakes, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Dec. 21, 1962, Ser. No. 246,537

7 Claims. (Cl. 10227) This application is a continuation-in-part of U. S. patent application Serial No. 33,716, filed June 3, 1960, now abandoned.

The present invention relates to a novel delay-initiation cord for use in delay blasting and to a novel blasting assembly.

It has been generally recognized in blasting practice that improved results are obtained when the charges in all the boreholes for the blast are not initiated simultaneously, but are initiated in sequence and at precise intervals of time. Such non-simultaneous initiation, usually referred to as delay blasting, provides greater and more efficient blasting action, i.e., both the amount of material, or burden, blasted in one operation and the degree of fragmentation are substantially improved. This substantial improvement over the instantaneous method of initiation is due primarily to the fact that the burden loosened by the initial charge has moved out from the face a distance before the next charge is initiated. Thus, in effect, a peeling-01f action is obtained. Greatly lessened ground vibration is another desirable feature of delay blasting. A further advantage is that owing to the greater burden movement, the cost of drilling and of explosives are reduce-d considerably.

Several means have been employed to accomplish the desired delayed initiation of the explosive charges. One means involves a mechanical arrangement for controlling the application of electrical energy to the individual electric initiators. Another means is a delay electric initiator in which the delay interval is provided by the burning of a pyrotechnic composition (a delay charge) interposed between the electrically ignited charge and the primer charge of the initiator. A third means is the positioning of a delay connector in a line of detonating fuse (Primacor leading to the explosive charge. A fourth means involves the low-energy connecting cord as described in U. S. 2,982,210, which transmits a detonation impulse to a delay connector or to a delay initiator.

All of the foregoing procedures sulfer from certain serious shortcomings. The electrically initiated devices possess the disadvantage of being subject to accidental firing by stray currents, lightning, or radio frequency energy. Further, the delay intervals provided by the electric initiators now commercially available are not always as accurate as might be desirable. Delay blasting with detonating fuse and delay connectors, while free of the hazards associated with electrical firing means, is, nevertheless, far from an ideal method. One particularly disturbing aspect of this method is the considerable noise and brisance produced by the fuse upon detonation. Aside from the annoyance to individuals in the vicinity which this noise creates, the attendant brisance also necessitates careful positioning of the fuse, often with elaborate and expensive shielding methods, to prevent cut-offs or severing of the fuse.

Further, the delay connectors, in every case of which I am aware comprise units which are manufactured in a few standard sizes and impose upon the blaster a limited scope of operation. Moreover, owing to their tendency to fail in operation, such devices commonly are employed in parallel in an assembly generally in a secondary or supplementary trunk line of detonating fuse in the hope if one assembly of cord and connectors does not function properly, the other probably will. Further, many of the ice connectors and delay assemblies presently available are of the one-way type and necessitate a precise order of rotation. The low-energy connecting cord, while free of objectionable brisance, necessitates careful handling of the cord and connectors or initiators so that the two will not become separated. Additionally, the low-energy assemblies also are manufactured in a few standard sizes which limit the scope of blasting operation. All of the aforementioned methods of producing a delayed blast require expensive and elaborate accessories and great caution and careful supervision in loading the explosive charges and in giaking the necessary and tedious connections for the ast.

A most serious shortcoming of delay blasting means used heretofore, each of which relies upon delay con nectors and/0r delay detonators, is that despite every manufacturing precaution, delay periods of supposedly equal connectors or detonators are not only unequal, but frequently may vary appreciably from the desired time. Thus, while the average delay time for any large sampling may be close to the design interval, many individual units may have delay times appreciably greater or less than the design interval. Consequently, the danger exists that a detonator or connector having the maximum delay time of one delay series may have the same or even a longer delay time than that having the minimum delay time in the next one or several delay series. If such detonators or connectors are used together in the field, obviously the desired blasting cannot be achieved, in fact harmful ac tion may occur.

In accordance with this invention, a means for delay blasting is provided in which all of the foregoing disadvantages are avoided. More particularly, in accordance with this invention, a delay-initiation cord characterized by uniform low velocity, low brisance and the production of little noise is provided which comprises a continuous core of a defiagrating composition encased in snug peripheral engagement by a flexible sheath having a tensile strength of at least about 25 p.s.i., the loading of the defiagrating composition in the core being from 0.1 to 5 grains per foot, the said core of defiagrating composition being characterized by a uniform deflagration velocity of from 100 to 650 meters per second.

More specifically, the delay-initiation cord of this invention comprises a core of defiagrating composition encased in snug peripheral engagement by a sheath of flexible material having a tensile strength of at least 25 p.s.i., said composition being selected from the group consisting of (A) a composition containing from to 98 parts by weight lead azide and from 25 to 2 parts by weight nonexplosive diluent, said core having a packed density of at least 3.5 g./cc.; (B) a composition selected from the group consisting of (1) tetracene and (2) mixtures of the lead salt of dinitro-o-cresol with a member of the group consisting of (a) potassium chlorate and tetracene, (b) potassium chlorate and pentaerythritol tetranitrate, (c) potassium chlorate and lead styphnate, and (d) potassium chlorate and diazodinitrophenol; and (C) a composition containing from about 10 to about parts by weight lead azide and from about 90 to about 10 parts by weight of an explosive composition selected from the group consisting of nitromannite, pentaerythritol tetranitrate, tetracene, and diazodinitrophenol; said core of deflagrating composition being at a packed density of at least 3.5 -g./ cc. and being characterized by a uniform deiiagration velocity of from 100 to 650 meters per second.

While the deflagration velocity for the defiagrating composition is given as 100 to 650 meters per second, this is equivalent to a burning rate of from about 3.0 to 0.5 millisecond per foot.

By the term deflagration composition is meant that the composition, when properly initiated, propagates a defiagration stimulus, i.e., a stimulus produced by a chemical reaction characterized by the vigorous evolution of heat and sparks or flame and moving through the material deflagrating at a speed less than that of sound, generally at a speed less than about 2000 meters per second.

The term packed density as used herein denotes the density of the core after the necessary steps in the processing of the cord have been completed.

In a preferred embodiment of this invention, the core of deflagrating composition is at a loading of about 0.1 to 2 grains per foot and the composition comprises about 75 to about 98 parts by weight of lead azide and 25 to about 2 parts by weight of a diluent such as a non-explosive composition; e.g., graphite, calcium stearate, methyl cellulose, polychlorinated polyphenols, modified fatty esters, polyisobutylene, dextrin, wax, talc, neoprene, lead carbonate, red lead, ammonium phosphate, polyvinyl acetate, and chlorosulfonated polyethylene. The packed density of the core must be at least 3.5 g./ cc. and and preferably from about 3.7 to about 4.5 g./cc. To insure that the stimulus transmitted by the cord is of deflagrating nature, initiation of the core should be by a low-energy shock such as is provided when the cord is actuated through its sheath by detonating fuse, i.e., by wrapping it around Primacord, or side-printed by an initiator, i.e., the initiator is taped side-by-side to the cord rather than end-to-end in the conventional manner. However, cords whose cores have a packed density of greater than about 4.3 g./ cc. can be initiated at the desired low velocities by initiators taped end-to-end.

In another preferred embodiment of this invention, the core is of a normally defiagrating composition such as tetracene; a mixture of the lead salt of dinitro-ocresol, potassium chlorate and PETN; a mixture of the lead salt of dinitro-o-cresol, potassium chlorate and lead styphnate, or a mixture of the lead salt of dinitro-ocresol, potassium chlorate, and diazodinitrophenol. These cords are reliably initiated at low, defiagrating velocities either when attached to an electric or non-electric initiator in the conventional manner (end-to-end) or when knotted or coiled about or taped to detonating fuse.

In still another preferred embodiment of this invention, the deflagrating core comprises from about 10 to about 90 parts by weight of lead azide, the balance of the core composition being a normally explosive composition such as PETN, nitromannite, tetracene, or diazodinitrophenol, and the loading of the core is preferably from about 0.1 to about 1.5 gr./ft. In this case, as in the case of the lead azide/diluent cores, the density of the core should be high, e.g., above 3.5 g./cc., as provided when the cord is prepared by swaging, and initiation should be through the sheath, either by wrapping the cord around Primacord and initiating the Primacord or by side priming with a conventional explosive initiator.

The delay-initiation cord of this invention can be used as the delay means in a delay blasting assembly comprising a plurality of boreholes loaded with high explosive charges, a downline of detonating fuse extending from the ground surface to the desired depth within the borehole (usually the full length of the boreholes), a plurality of lengths of delay-initiation cord connecting said downlines in a predetermined sequential relationship and a means for initiating the assembly, at least one end of said lengths of delay-initiation cord being capped by a metal shell containing an explosive charge initiatable by the deflagration impulse of said cord and of suificient strength to initiate detonating fuse.

Alternatively, the delay-initiation cord of this invention can be used in a delay blasting assembly as the downline extending into the borehole with the downlines connected in the predetermined sequential relationship by detonating fuse, The length of the downline in each borehole is directly proportional to the delay time desired between initiation of the assembly and actuation of the charges in the borehole. In this assembly, one end of the delay-initiation cord is attached to the detonating fuse, which initiates the downline, and the other end is capped by a shell containing an explosive train initiatable by the deflagration impulse from said cord and producing an impulse of sufiicient strength to actuate an initiator for the charges in the borehole.

The accompanying figures illustrate various practical embodiments of this invention. In the drawings,

FIGURE 1 is a schematic top view of a quarry face and shows a typical blast layout in accordance with my invention,

FIGURES 2, 3, and 4 show various alternative means of connecting my delay-initiation cord to detonating fuse,

FIGURE 5 is a schematic representation in cross section of the delay-initiation cord,

FIGURE 6 is a sectional view of a borehole showing a typical blast layout in accordance with my invention.

Referring now to FIGURE 1 for more detailed explanation of the assembly of my invention, the edge of the quarry face is indicated at F. Boreholes indicated by B are drilled vertically in the face in three rows, each row having seven holes spaced apart a distance of 20 feet. Each borehole, which is loaded with explosive charges and has inserted its full depth a downline of detonating fuse as the primer, is connected to the adjacent boreholes by a length of delay-initiation cord A and each row of holes is connected to the one originally initiated. In this case, a second parallel length of the same cord; A, has also been employed to provide maximum assurance against failures or cutoffs. Cords A and A are initiated at point I by initiator E, which in this case is an electric initiator. Assuming that cords A and A have a burning rate of 1 millisecond per foot and are 20 feet long, the charges in holes B and B are initiated after a time delay of 20 milliseconds after initiation of the charges in the initial borehole B the charges in holes B B and B after 40 milliseconds, and so on until all the holes have been shot. Obviously, if a longer delay interval, e.g., 22 or 25 milliseconds, if desired, the length of the delay-initiation cord will be chosen accordingly.

In FIGURE 2, P indicates a length of detonating fuse provided as the primer or down-line for the explosive charges in a borehole. Delay-initiation cord A is con nected to fuse P through initiator G which is securely attached side-by-side to the fuse by tape T. A second length of cord A is knotted around fuse P at a point below the initiator G and extends to the next borehole. Initiator G on actuation by cord A initiates fuse P, which in turn initiates the second length of cord A knotted around it. Cord A then relays the delay initiation stimulus to the corresponding initiator G in the adjacent borehole.

In the assembly of FIGURE 3, devised to relay the initiation stimulus in either direction, P, G, T, and A are as in the assembly of FIGURE 2 except that the initiators are attached perpendicularly to fuse P rather than side-by-side. In this case, if the delayed initiation stimulus comes through cord A, initiator G will initiate fuse P and cord A will carry the delayed initiation stimulus to the adjacent borehole. On the other hand, if the initiation stimulus comes from the direction of cord A, initiator G will initiate fuse P and the delayed initiation impulse will be directed along cord A. For convenience, the initiators may be contained in a plastic or metal shell having a transverse hole to receive detonating fuse.

FIGURE 4 shows a modification of the two-Way as sembly of FIGURE 3 wherein the initiators G and G are positioned side-by-side and parallel to the fuse P rather than perpendicular thereto.

In the delay-initiation cord illustrated by FIGURE 5,

M is a continuous core of a deflagrating composition, N is a sheath of a ductile metal or a woven textile such as high denier rayon, and 0 represents a layer of waterproofing and strengthening material, e.g., a plastic and/ or textile covering.

In FIGURE 6, B represents a vertical borehole containing conventional cap-sensitive explosive units U, the bottom-most charge being indicated at S. In intimate relationship with the bottom unit is initiator G which is attached to delay-initiation cord A. This delay-initiation cord A extends from the bottom of the borehole past explosive units U and through stemming T to the surface of the borehole where it is attached to detonating fuse P connecting this borehole with other boreholes in the blasting assembly. The delay-initiation cord may extend only from the bottom of the borehole to the top or it may extend from the bottom of the borehole to a point remote from the top of the borehole, or a long length of the cord can be coiled or looped so that a long length of the cord can be present in the borehole. In any event, the interval or delay between actuation of the cord by the detonation fuse and the time when the deflagration stimulus transmitted by the cord actuates initiator G in the borehole is directly proportional to the length of delay-initiation cord used. For example if the length of delay-initiation cord within the borehole is 20 feet and the burning rate of the cord is 1 millisecond per foot, the delay between the time when the cord is actuated by the detonating fuse and the time When the deflagration stimulus is transmitted to initiator G Will be 20 milliseconds. If a different delay interval is desired, the length of the delay-initiation cord will be chosen accordingly. For example, a 20 millisecond interval may be desired between firing of this borehole and firing of the charges in the next borehole in the round in which case the length of delay-initiation cord in the next borehole would be 40 feet. Since the detonating fuse propagates the initiation impulse at a velocity of above 5000 meters per second, initiation of the two lengths can be considered essentially simultaneous, so that there will be a 20 millisecond interval (40 milliseconds minus 20 milliseconds) between actuation of the charges in the first borehole and actuation of charges in the second borehole.

The delay-initiation cords of this invention are prepared by filling the tubular sheath which preferably is of a ductile metal such as of lead or aluminum, with the desired defiagratin-g agent and subsequently drawing or swaging the sheath to reduce the diameter and to increase the density of the core. After the drawing or swaging step, the cord may be covered with a layer of waterproofing and reinforcing material such as a bituminous coating, spirally applied yarn, a wax finish, or a single extruded coating of a thermoplastic or thermosetting resin, preferably polyethylene or polyvinyl chloride. Alternatively, the tubular sheath may be woven of fibers such as of heavy denier (e.g., about 300 denier) rayon, cotton, or nylon.

For cords containing lead azide as a major constituent of the core composition, I have found that swaging of the tubular sheath gives a cord of more uniform deflagrating characteristics than does drawing since by this method, wherein the tube is struck by a large number of successive blows by a pair of shaped dies, higher core densities can be achieved. As further insurance of obtaining the high densities necessary particularly for core compositions containing lead azide, the fill density of the core should be at least about 2.4 g./cc. and preferably should be greater than 2.7 g./cc. since with this fill density, the density of the core can readily be increased to the 3.5 g./cc. required for reliable propagation of a deflagration stimulus. As noted above, to insure propagation of a deflagration stimulus with lead azide compositions it is also necessary that the composition contain from about 2 to about 25% of a diluent. Exemplary diluents include non-explosive compositions such as graphite, calcium stearate, methyl cellulose, polychlorinated polyphenols, modified fatty esters, polyisobutylene, dextrin, wax, talc, neoprene, lead carbonate, red lead, ammonium phosphate, polyvinyl acetate, chlorosulfonated polyethylene, and the like. Although cores containing higher percentages of lead azide can propagate a deflagration stimulus when at high densities, i.e., at densities greater than about 4.3 g./cc., when initiated by side priming or by wrapping around Primacord, these compositions do not reliably propagate a deflagration stimulus at lower densities and, accordingly, may propagate either a deflagration or detonation stimulus. When more than about 25% of a nonexplosive diluent is present in the core compositions, the velocity at which an impulse is propagated becomes so slow as to be unreliable for precision blasting operations. Within the specified ranges however, the cords propagate a deflagration stimulus at a uniform, precise rate.

The following examples illustrate specific embodiments of the delay-initiation cord of this invention.

EXAMPLE 1 A series of lead-sheathed cords containing various lead azide/ diluent compositions were prepared by loading lead tubes having an outside diameter of about 0.312 inch, and an inside diameter of about 0.157 inch, with these compositions at a filling density of approximately 2.4 g./ cc. and reducing the diameters of the tubes by swaging. In each case, the lead azide used was commercially available dextrinated lead azide which has a lead azide content of 93%. The cords, their core compositions and loadings and their velocity of deflagration are summarized in the following table (Table 1), wherein lead azide denotes the abovedescribed dextrinated lead azide. In each case, the cords were initiatedby wrapping them around Primacord and initiating the Primacord. In each case after the cords were swaged, the packed density of each core Was at least 3.5 g./cc. and, generally, about 3.7 g./ cc.

Table 1 Core Composition Core Load- Velocity,

mg (gin/ft.) m./sec.

1 600 2 060 1 330 99/1 lead azide/Bareco wax 1 380 Do 2 390 98/2 lead azide/Bareeo wax 1 280 97/3 lead azide/Bareeo wax 1 190 96/4 lead azide/Bareeo wax 1 120 95/5 lead azide/Bareco wax 1 100 98/2 lead azide/Neoprene" 1 490 D0 2 540 98.8/1.2 lead azide/methyl cellulose 1 620 92/8 lead azide/polyvinyl acetate 1 480 98.5/1.5 lead azide/chlorosulfonated polyethylone 1 440 Do 2 450 95/5 lead azide/diabasic lead phosphite 1 620 95/5 lead azide/lead earbonate. l 635 D0 2 575 90/10 lead azide/lead carbonate- 1 600 /15 lead azide/lead carbonate- 2 580 80/20 lead azide/lead carbonate. 1 355 /10 lead azide/red lead 1 625 98.8/L2 lead azide/polyisobutylene. 1 480 97/3 lead azide/conductive wax 1 490 97/3 lead azide/polychlorinated polyphenol 1 270 99/1 lead azide/polychlorinated po1yphenol l 455 90/10 lead azide/ammonium phosphate 1 430 90/10 lead azide/talc 1 390 97/3 lead azide/fatty ester. 1 230 Do 2 240 98/2'lead azide/ Glycowa 1 240 Do 2 280 98/2 lead azide/wax l 260 99.5/0.5 lead azide/Wax 1 455 When cords were prepared using higher purity lead azide, i.e., colloidal lead azide (99% lead azide) and a composition having a lead azide content of 98% as the sole component of the core and initiated by Primacord, predominately high detonating velocities (3900-4000 meters/second) were exhibited, even at core loadings of less than /2 gr./ft., in swaged lead tubes.

' In order to evaluate the relationship of core density and method of initiation to the deflagration velocity of the cord, a series of cords were prepared as in Example 1 by swaging. At the same time, a series of cords were prepared for comparative purposes using the same core loadings and compositions, however, in these cords prepared for comparative purposes, the reduction of lead tubes containing the lead azide/diluent was accomplished by drawing through dies so that the packed densities of the cores were less than the 3.5 g./ cc. value, which I have found necessary to insure that a defiagration stimulus is transmitted by the cord. Initiation of the cords was efiected (a) by butting the cord against a conven-- tional blasting cap (end-to-end) and (b) by wrapping the cords about a length of Primacord. The cords, their core compositions and loadings and their velocity of deflagration (or detonation) are summarized in the following table (Table 2). As in Table 1, the lead azide referred to is dextrinated lead azide having a lead azide content of 93 8 EXAMPLE 3 In order to evaluate the performance of delay-initiation cord on a scale employed in field use, a 1000 foot length of delay-initiation cord was prepared by the swaging technique of Example 1, the core composition being dextrinated lead azide (93% lead azide) at a loading of 1 gr./ ft., a load calculated to give a burning rate of about 0.6 Ins/ft. The cord was sampled at 38 intervals along its entire length, 57 and 117 foot lengths being cut. The average burning rate of the lengths was 0.638 ms./ft., the highest value being 0.669 ms./ft. and the lowest value being 0.613 ms./ft., a variation of only 0.056 ms./ft. The corresponding average deflagration velocity was 477.4 m./ sec., the lowest value being 465.7 m./ sec. and the highest value 497.3 m./sec., a variation of only 29 m./sec.

EXAMPLE 4 The following lead azide/nitromannite compositions Table 2 Velocity, m./see.

Composition Preparation Loading of 1 g'rJft. Loading of 2 grJit.

Method Cap Ini- Primacord Cap Ini- Primacord tiation Initiation tiation Initiation 80/20 lead azide/barium peroxide Drawing." 2, 400 2, 500 2, 600 2, 900 o S\vaging 630 600 3, 140 60 97/25 lead azide/B areco Wax. Drawing" 2, 600 2, 720 2, 850 2, 880 D SWaging 310 330 2, 960 320 98/2 lead azide/Ne0prene Drawing 2, 650 2,820 2, 770 2, 850 Swaging 3, 400 490 3, 720 540 92/8 lead azide/polyvinyl aceta Drawin 2, 300 2, 420 2, 440 2, 650 0 Swagin t 3, 280 480 3, 430 470 95/5 lead azide/lead earbonate Drawing 2, 600 2, 480 2,580 2, 580 Do SWaging 3,370 635 3, 390 575 90/10 lead azide/lead carbonate. Drawing..- 2, 600 2, 200 2, 820 2, 460 Do Swaging.... 3, 250 600 3, 175 570 98.8/l.2 lead azide/polyisobutylene Drawing. 2, 540 2, 700 2, 880 2, 900 D0 SwagingM" 3, 315 480 3, 315 510 97/3 lead azide/conductive wax Drawing 2, 680 2, 750 2, 880 2, 820 Do Swag1ng 3, 430 490 3, 470 470 Cord side-primed by conventional electric blasting cap demonstrated essentially the same velocities as cord initiated by Primacord.

As may be seen from the table, when lead azide compositions are used as the deflagrating core in the delaywere prepared in swaged 0.073 inch diameter lead tubes (core load of 1.4 gr./ft.; packed density above 3.5 g./cc.).

Lead azide/nitromannite initiation cord of this invention, (a) a diluent must be 40 90/10 present, (b) the density of the cord must be at least 3.5 80/20 g./cc., i.e., the cord should be prepared by swaging, or /50 pressurized by other means such as hydrostatic pressure, 40/ and (c) initiation of the cord should be by a low-energy 50 25/ shock such as is provided when the cord is wrapped around Primacord or when side-primed by an initiator.

EXAMPLE 2 In general velocities of the cords were in the range of 300550 m./sec. when the cords were initiated by Primacord. Typical, average velocity measurements for 75/25 nitromannite/lead azide swaged in 0.073 diameter lead sheaths (core loading of 1.4 gr./ ft.) were about 492 m./ sec.

60 Similar results were obtained for lead azide/fine PETN Table 3 cores as shown below at loadings of 0.5 and 1 gr./ft. were tested in swaged lead sheaths. Loading, gr./ft. Lcengithfgf Time, Velocity, Burninlgtrate,

or ms. m. s c. s.

m Lead azide/PETN 2 1. 25 487 0.63 2 1.26 485 0.03 70 g 3; l; :33 32 Tests on /20, /10, 95/5, and 98/2 lead azide/tetra- %g g. 32; 8.2g cene mixtures indicated that material in drawn lead tub- 20 51 487 ings transmitted a deflagration stimulus when initiated by 20 12.86 9 Primacord and that material swaged in lead at core 75 loadings of less than 1 gr./ft. burned at low deflagration velocities both for Primacord and end-to-end cap ini- Table 6 tiation. Results for 90/10 lead azide/tetracene compositions are shown in Table 4.

Composition l'zoatlififingg Velocity, Bfirrimg gr. in. see. a e, Table 4 Lead salt of Potassium ins/ft.

dinitro-o-cresol chlorate Outside Velocity, Burning rate 2 Loading, grJft. diameter, m./see. ms./it. 2 11101165 0. 3 170 1. 79 30 1.3 225 3g 30 0. 04 2 s 15 743 30 0. 34 233 1. 31 O. 105 368 0.829 30 0 21 210 1 45 0. 073 335 0. 910 30 1 201 1 52 30 0.03 180 1. 09 40 2.0 235 1.30 2 43 1 0 0. EXAMPLE 5 50 0.0 212 1.44 50 3.3 229 1.33 Delay-lmtiation cords were prepared by the swagmg 50 1.9 220 1.39 d d d E l 1 t t t 50 0.97 228 1.34 proce ure escri e 1n xamp e except a e racene 50 55 239 L28 alone was used as the core composition. The cords func- 50 5. 0 217 1.40 tioned as shown in Table 5, below. 88 i1; i ii 60 0.67 209 1.46 Table 5 50 0.49 210 1. 5

L d m dOut-sitde Imt t Burning Velocity, 021 ing. gr. iame er ia or ra e, in. sec.

inches ms./it. EXAMPLE 7 O 150 Cap L142 267 A series of cords containing various mixtures of the 0.150 rimacord 1 2 2% lead salt of dinitro-o-cresol, potassium chloride, and tetra- 0.105 a 2 0.105 L174 260 cene were prepared by the drawing and swaging methods 0. 073 an 1.1g; of Examples 1 and 6. The composition and loading of 3:8? gg i fffi 5:8 321 the cores, the method used in their preparation, the def- 0.051 Pr1ma 0 d-- .865 352 lagratlon velocitles and the burnmg rates of the cords are summarized in Table 7.

Table 7 Composition Burning Loadin Preparation Velocity, Rate, Lead Salt of Potassium TetragrJft. Method m./sec. msJft.

1,2-dinitro- Chlorate cene o-cresol 10 2 Drawing- 290 1. 05 40 10 1 do 277 1.10 40 10 3 283 1.11 35 15 3.35 287 1.00 35 15 0.94 292 1.04 5 3.05 298 1.02 45 5 2.19 279 1. 09 45 5 1. 203 1.16 45 5 1.07 205 1.15 45 5 0.05 251 1.21 40 10 2.85 225 1.36 40 10 1.95 210 1. 40 40 10 0. 95 197 1.55 40 10 0. 93 Swaging 241 1. 26 40 10 0.54 do 242 1.20 40 10 0.50 do 248 1.23

EXAMPLE 6 EXAMPLE 8 A delay-initiation cord was prepared using 50/40/10 mixtures of the lead salt of dinitro-o-cresol/potassium chlorate/fine PETN at a loading of 0.56 gr./ft. in a drawn lead tube. When the cord was initiated by a conventional electric blasting cap (end-to-end initiation) the cord propagated a deflagration stimulus at a velocity of 22S m./sec. (1.34 m./ft.).

EXAMPLE 9 Delay-initiation cords were prepared by the drawing technique with 1 and 2.3 gr./ft. core loadings of 50/40/10 lead salt of dinitro-o-crcsol/ potassium chlorate/ lead styphmate and were initiated by end-to-end priming with an electric blasting cap. The cords burned at deflagration velocities of 240250 m./sec.

EXAMPLE The defiagrat-ion velocity of a cord containing a 50/ 40/ 10 lead salt of dinitro-o-cresol/ potassium chlorate/ diazodinitrophenol composition at a loading of 1.17 gr./ft. in drawn lead tubing was 227 m./sec. when initiated by end-to-end priming by an electric blasting cap. The velocities of swaged cords having core loads 1.67 and 0.83 gr./ft. of the composition varied from about 231 246 m./ sec.

The delay-initiation cord of this invention is characterized by uniform low velocity, low brisance, and the production of little noise. Therefore, the cord is particularly advantageous for use in applications where shielding cannot be provided, for example in bottom-hole priming where the noise and brisance inherent in detonating fuse and delay connectors cannot be tolerated. The low brisance of the cord eliminates the possibility of simultaneous deflagration of all the cord composition within a coiled length, and the deflagration generally is propagated through the core without damaging the countering at all. Since the cord is flexible, the blasting operator may choose the length of delay-initiation cord appropriate to the amount of time delay desired and, if necessary, coil or bend the cord to fit the spatial confines of his blasting assembly. This continuity of propagation even through a knotted or kinked section is surprising in view of the known failure of ignition-transmission lines which depend upon the oversize conduit for burning combustible materials to propagate through knots or kinks.

It will be apparent from the foregoing that the delayinitiation cord of this invention fills a void in the art in that it provides a highly efficient and dependable flexible delay-initiation cord which makes possible the elimina tion of the costly and undependable delay devices heretofore considered necessary and provides highly elficient and dependable delay action at a cost appreciably below those in present-day conventional practice.

The present invention has been described in detail in the foregoing. However, as will be apparent to those skilled in the art, variations are possible without departure from the scope of the invention.

What is claimed is:

1. A delay-initiation cord comprising a core of def lagrating composition containing from 75 to 98 parts by weight lead azide and from to 2 parts by weight non explosive diluent, encased in a sheath of a flexible material having a tensile strength of at least 25 pounds per square inch, the loading and the packed density of said deflagrat ing composition being from about 0.1 to 2 grains per foot and at least 3.5 g./cc. respectively, and said core of deflagrating composition being characterized by a uniform deflagration velocity of from 100 to 650 meters per second.

2. The cord as in claim 1 wherein said non-explosive diluent is selected from the group consisting of graphite, calcium stearate, methyl cellulose, polychlorinated polyphenols, modified fatty esters, polyisobutylene, dextrin, wax, talc, neoprene, lead carbonate, red lead, ammonium phosphate, polyvinyl acetate, and chlorosulfonated poly ethylene.

3. The cord of claim 1 wherein said sheath is of ductile metal and the core of defiagrating composition is at a packed density of about from 3.7 to 4.5 g./cc.

4. A delay-initiation cord comprising a core of deflagrating composition selected from the group consisting of 1) tetracene and (2) mixtures of the lead salt of dinitro-o-cresol with a member of the group consisting of (a) potassium chlorate and tetracene, (b) potassium chlorate and pentaerythritol tetranitrate, (c) potassium chlorate and lead styphnate, and (d) potassium chlorate and diazodinitrophenol, encased in a sheath of a flexible material having a tensile strength of at least 25 pounds per square inch, the loading of said defiagrating composition being from about 0.1 to 5 grains per foot, and said core of defiagrating composition being characterized by a uniform deflagration velocity of from 100 to 650 meters per second.

5. The cord of claim 4 wherein said sheath is of ductile metal.

6. A delay initiation cord comprising a core of deflagrating composition containing from about 10 to about parts by weight lead azide and from about 90 to about 10 parts by weight of an explosive composition selected from the group consisting of nitromannite, pentaerythritol tetranitrate, tetracene, and diazodinitrophenol, encased in a sheath of a flexible material having a tensile strength of at least 25 pounds per square inch, the loading and the packed density of said defiagrating composition being from about 0.1 to 1.5 grains per foot and at least 3.5 g./ cc. respectively, and said core of defiagrating composition being characterized by a uniform deflagration velocity of from to 650 meters per second.

7. The chord of claim 6 wherein said sheath is of ductile metal.

References Cited by the Examiner UNITED STATES PATENTS 2,175,249 10/39 Burrows et al 14924 2,239,123 4/41 Stoneking 102--23 2,865,726 12/58 Jenkins et a1. 149-35 2,923,239 2/60 Andrew et a1. 10227 2,980,019 4/61 Noddin 102-28 2,982,210 5/61 Andrew et a1. 102-27 2,992,611 7/61 Felch 102-22 FOREIGN PATENTS 731,108 6/ 55 Great Britain.

SAMUEL FEINBERG, Primary Examiner. 

4. A DELAY-INITIATION CORD COMPRISING A CORE OF DEFLAGRATING COMPOSITION SELECTED FROM THE GROUP CONSISTING OF (1) TETRACENE AND (2) MIXTURES OF THE LEAD SALT OF DINITRO-O-CRESOL WITH A MEMBER OF THE GROUP CONSISTING OF (A) POTASSIUM CHLORATE AND TETRACENE, (B) POTASSIUM CHLORATE AND PENTAERYTHRITOL TENANITRATE, (C) POTASSIUM CHLORATE AND LEAD SYPHNATE, AND (D) POTASSIUM CHLORATE AND DIAZODINITROPHENOL, ENCASED IN A SHEATH OF A FLEXIBLE MATERIAL HAVING A TENSILE STRENGTH OF AT LEAST 25 POUNDS PER SQUARE INCH, THE LOADING OF SAID DEFLAGRATING COMPOSITION BEING FROM ABOUT 0.1 TO 5 GRAINS PER FOOT, AND SAID CORE OF DEFLAGRATING COMPOSITION BEING CHARACTERIZED BY A UNIFORM DEFLAGRATION VELOCITY OF FROM 100 TO 650 METERS PER SECOND. 